Eulhae Ga

Influenza D virus (IDV) is an emerging orthomyxovirus with cattle as its principal reservoir, and D/Yama2019‐lineage viruses have become dominant in East Asia. Although IDV has been detected in Korean cattle, the genomic identity, phylogenetic placement, and regional evolutionary relationships of circulating Korean strains have not been defined. To address these gaps, nasal swabs were collected from 578 cattle with mild respiratory signs on 157 farms across eight provinces in South Korea during 2022–2023 and screened by RT‐qPCR targeting the PB1 gene. Positive samples underwent complete genome sequencing of all seven segments, followed by maximum‐likelihood and Bayesian phylogenetic analyses, discrete phylogeographic inference using a Bayesian stochastic search variable selection (BSSVS) model, and positive selection analyses. Six samples from three farms were IDV‐positive (sample‐level positivity: 1.04%; farm‐level positivity: 1.9%), all from 8‐to‐10‐month‐old calves. Phylogenetic analysis of all seven genomic segments placed all six Korean strains within the D/Yama2019 lineage with strong bootstrap support (99%–100%), forming a monophyletic cluster more closely related to Chinese than to Japanese D/Yama2019 reference strains. No phylogenetic evidence of reassortment was detected. Bayesian time‐scaled analysis estimated the most recent common ancestor of the Korean strains at ~2018.1–2020.1 across all seven segments. HEF‐based BSSVS analysis suggested a China‐to‐South Korea transition within the sampled dataset (posterior probability (PP) = 0.982; Bayes factor (BF) = 163.67), although this result should be interpreted in light of the small number of Korean sequences and the single‐segment basis of the phylogeographic analysis. Positive selection analyses revealed limited, method‐dependent signals without support from the fixed effects likelihood model, and Korean‐associated amino acid substitutions in PB1, P3, NS1, and NS2 were interpreted as lineage‐associated molecular signatures rather than evidence of adaptive evolution. These findings provide a whole‐genome baseline for IDV surveillance in South Korea and support continued longitudinal monitoring to clarify the persistence and transmission dynamics of D/Yama2019‐lineage viruses in the region.

The NS1 influenza protein of influenza A virus is a viral nonstructural protein encoded by the NS gene segment that has multiple accessory functions during viral infection. In recent years, the major role ascribed to NS1 has been its inhibition of host immune responses, especially the limitation of both interferon (IFN) production and the antiviral effects of IFN‐induced protein. We isolated an equine influenza virus with a naturally truncated NS1 gene in our previous study. In this current research, we inserted this partially truncated NS gene into the H₃N₂ canine influenza virus using reverse genetics to develop a live attenuated vaccine strain. To evaluate whether the developed strain is suitable as a live vaccine candidate, we compared its replication kinetics with wild‐type virus in MDCK cells and specific pathogen‐free eggs. Additionally, we investigated host antiviral gene expression, viral replication in the respiratory system, and associated lung tissue damage in mice experiments. To confirm the efficacy of the vaccine candidate, we evaluated the immunogenicity and protectivity of the developed vaccine strain against canine influenza H₃N₂, compared with a commercial inactivated vaccine. Through these experiments, it was confirmed that the naturally truncated NS1 inserted virus has sufficient potential as a live vaccine candidate, and we hopefully expect that this study would make a great contribution to the development of a live vaccine for canine influenza H₃N₂.

COVID-19 is caused by severe acute respiratory syndrome virus type 2 (SARS-CoV-2), which can infect both humans and animals. SARS-CoV-2 originated from bats and can affect various species capable of crossing the species barrier due to active mutation. Although reports on reverse zoonosis (human-to-animal transmission) of SARS-CoV-2 remain limited, reverse zoonosis has been reported in many species such as cats, tigers, minks, etc. Therefore, transmission to more animals cannot be ruled out. Moreover, the wide distribution of SARS-CoV-2 in the human population could result in an increased risk of reverse zoonosis. To counteract reverse zoonosis, we developed the first COVID-19 subunit vaccines for dogs, which are representative companion animals, and the vaccine includes the SARS-CoV-2 recombinant protein of whole S1 protein and the receptor-binding domain (RBD). A subunit vaccine is a vaccine developed by purifying only the protein region that induces an immune response instead of the whole pathogen. This type of vaccine is safer than the whole virus vaccine because there is no risk of infection and proliferation through back-mutation of the virus. Vaccines were administered to beagles twice at an interval of 3 weeks subcutaneously and antibody formation rates were assessed in serum. We identified a titer, comparable to that of vaccinated people, shown to be sufficient to protect against SARS-CoV-2. Therefore, the vaccination of companion animals, such as dogs, may prevent reverse zoonosis by protecting animals from SARS-CoV-2; thus, reverse zoonosis of COVID-19 is preventable.